Commercial switchable glazing devices, also commonly known as smart windows and electrochromic window devices, are well known for use as mirrors in motor vehicles, aircraft window assemblies, sunroofs, skylights, and architectural windows. Such devices may comprise, for example, active inorganic electrochromic layers, organic electrochromic layers, inorganic ion-conducting layers, organic ion-conducting layers and hybrids of these sandwiched between two conducting layers. When a voltage is applied across these conducting layers the optical properties of a layer or layers in between change. Such optical property changes typically include a modulation of the transmissivity of the visible or the solar sub-portion of the electromagnetic spectrum. For convenience, the two optical states will be referred to as a bleached state and a darkened state in the present disclosure, but it should be understood that these are merely examples and relative terms (i.e., a first one of the two states is more transmissive or “more bleached” than the other state and the other of the two states is less transmissive or “more darkened” than the first state) and that there could be a set of bleached and darkened states between the most transmissive state and the least transmissive state that are attainable for a specific electrochromic device; for example, it is feasible to switch between intermediate bleached and darkened states in such a set.
The broad adoption of electrochromic window devices in the construction and automotive industries will require a ready supply of low cost, aesthetically appealing, durable products in large area formats. Electrochromic window devices based on metal oxides represent the most promising technology for these needs. Typically, such devices comprise two electrochromic materials (a cathode and an anode) separated by an ion-conducting film and sandwiched between two transparent conducting oxide (TCO) layers. In operation, a voltage is applied across the device that causes current to flow in the external circuit, oxidation and reduction of the electrode materials and, to maintain charge balance, mobile cations to enter or leave the electrodes. This facile electrochemical process causes the window to reversibly change from a more bleached (e.g., a relatively greater optical transmissivity) to a more darkened state (e.g., a relatively lesser optical transmissivity).
Ion conducting materials used in electrochromic windows are typically capable of adhering the two TCO layers to one another to form a multi-layer stack. Prior art ion conducting materials, however, suffer from certain limitations that impede the performance and durability of the electrochromic windows that encompass such ion conducting materials. Specifically, ion conducting polymers having high conductivity to ions such as lithium typically do not possess the mechanical properties necessary to endure physical stresses and strain placed on the multi-layer stack during its manufacture, its incorporation into a structure (e.g., an automobile, aircraft, or building), and/or its intended end-use environment (e.g., as an architectural window, sunroof, skylight, mirror, etc., in such a structure). Conversely, ion conducting materials capable of enduring significant physical stress without succumbing to adhesive or cohesive failure typically do not possess the electrochemical properties necessary to maintain high ionic conductivity over an extended period of time under variable environmental conditions.
Briefly, therefore, the present disclosure is directed to multi-layer electrochromic structures incorporating a cross-linked ion conducting polymer layer that maintains high adhesive and cohesive strength in combination with high ionic conductivity for an extended period of time.
One aspect of the present disclosure is an electrochromic structure comprising a cross-linked lithium-ion conducting polymer layer between opposing first and second substrates, the first substrate comprising a first electrochromic layer between the first substrate and the cross-linked lithium-ion conducting polymer layer, wherein, at room temperature, the cross-linked ion conducting polymer (i) is electrochemically stable at voltages between about 1.3 V and about 4.4 V relative to lithium, (ii) has a lithium ion conductivity of at least about 10−5 S/cm, and (iii) lap shear strength of at least 100 kPa, as measured at 1.27 mm/min at room temperature in accordance with ASTM International standard D1002 or D3163.
A further aspect of the present disclosure is a process for forming an electrochromic structure. The process of assembling an electrochromic multi-layer stack comprises (A) depositing a layer of an ion conducting polymer feedstock onto a first multi-layer stack, the first multi-layer stack comprising a first substrate and a first electrode layer, (B) laminating a second multi-layer stack comprising a second substrate and a second electrode layer to the first multi-layer stack to form an electrochromic multi-layer stack comprising, in succession, the first substrate, the first electrode layer, the ion conducting polymer feedstock layer, the second electrode layer, and the second substrate, the first electrode layer, the second electrode layer, or both comprising an electrochromic material; and (C) irradiating the electrochromic multi-layer stack to polymerize the ion conducting polymer feedstock, forming a cross-linked ion conducting polymer layer, wherein the cross-linked ion conducting polymer, at room temperature, (i) is electrochemically stable at voltages between about 1.3 V and about 4.4 V relative to lithium, (ii) has a lithium ion conductivity of at least about 10−5 S/cm, and (iii) lap shear strength of at least 100 kPa, as measured at 1.27 mm/min in accordance with ASTM International standard D1002 or D3163.
A further aspect of the present disclosure is an ion conducting polymer feedstock material having a viscosity of about 20,000 cP to about 50,000 cP, the ion conducting polymer feedstock material comprising between about 5 wt. % and about 50 wt. % monomer, oligomer, or a mixture of monomers and/or oligomers, an ionizable charge carrier, and a plasticizer. In one embodiment, the ion conducting polymer feedstock material is capable of being cross-linked to form a cross-linked ion conducting polymer, wherein the cross-linked ion conducting polymer at room temperature is characterized by (i) electrochemical stability at voltages between about 1.3 V and about 4.4 V, (ii) ionic conductivity of at least about 10−5 S/cm, and (iii) lap shear strength of at least 100 kPa, as measured at 1.27 mm/min in accordance with ASTM International standard D1002 or D3163.
Other objects and features will be described hereinafter.
Corresponding reference characters indicate corresponding parts throughout the drawings. Additionally, relative thicknesses of the layers in the different figures do not represent the true relationship in dimensions. For example, the substrates are typically much thicker than the other layers. The figures are drawn only for the purpose to illustrate connection principles, not to give any dimensional information.